High power, high frequency electron tube



Aug. 30, 1960 W. C. GRIFFITHS, JR., ET AL HIGH POWER, HIGH FREQUENCY ELECTRON TUBE Filed Oct. 27, 1958 'HUIUUUHHIUHHIHUHIII HHH(HHHHHHUUHUH Wm f HIGH POWER, HGH FREQUENCY ELECTRON TUBE William C. Gril'iiths, ir., Pottstown, and 1ra E. Smith, Lancaster, Pa., assignors to Radio Corporation ot America, a corporation of Delaware lliiied ct. 27, 1953, Ser. No. 769,646

3 Claims. (Cl. 313-247) This invention relates to a high power, high frequency electron tube having cylindrical electrodes and particularly to a novel and improved cathode support structure for such'a tube.

In certain high power electron tubes it is known to use a scrption-type getter .to occlude undesirable gases. Such a getter functions to absorb various gases contained within the electron tube when the getter material is raised to predetermined temperatures. it is also known to dispose such a getter structure at least partially within the cathode. However, according to prior art tube structures it is indeed diiiicult, if not impossible, to fabricate such cathode-getter combination structures due to the required order of assembling and processing the various tube parts.

High power electron tubes of the type described generally incorporate either conventional oxide coated or thoriated tungsten tilamentary cathodes. The oxide coated cathode is provided by depositing a mixture of, e.g., barium calcium, and strontium carbonates onto a metallic member. These carbonates are then converted .to the oxides of the respective metals by an activation process which involves heating the carbonates to an elevated temperature. When a thoriated tungsten iila nientary cathode is used, it is necessary to process the cathode by carbonizing the cathode filaments. This is generally done, e.g., by ashing the cathode in a benzene atmosphere. In the case of either type cathode it is necessary that the getter not be mounted within the cathode during processing thereof in order to prevent injury to the getter which might be occasioned by the elevated processing temperature. Moreover, in the case of a thoriated tungsten cathode, it is necessary .that the iilaments be mounted to their support members prior to the carbonizing thereof. Such carbonizing renders the thoriated tungsten iilaments too brittle to be handled for subsequent shaping `and mounting to a support structure.

It is therefore an object of this invention to provide a novel and improved electron tube wherein a getter structure can be mounted within a hollow cylindrical cathode after the cathode has been Xed in place and activated.

Another object of this invention is to provide an electron tube adapted to incorporate such yan improved cathode-getter structure and wherein a plurality of nes-ted cylindrical tube electrodes can be concentrically aligned by internal jigging and wherein the cathode support structure has improved radio frequency characteristics.

Briefly, according to our invention `an electron tube of the coaxial type comprises a stacked array of nested cylindrical electrodes. The cylindrical cathode is disposed concentrically around a first tubular conductor and is supported at one end thereof by a flange on the end of the tubular conductor. The other end of the cylindrical cathode is mounted to lthe end of a second tubular conductor which concentrically surrounds the iirst tubular conductor. A free-type sorption getter is mounted concentrically within the inner tubular conductor and eX- tends part way into the cathode.

In the drawings:

lFig. 1 is an axial section view of an electron tube incorporating a preferred embodimentof my invention; and

Fig. 2 is a :transverse section view taken on line 2--2 of Fig. l.

An electron tube 1t) is shown to comprise nested cylindrical cathode control grid, screen grid, and anode electrodes 12, 14, 16, and 1S, respectively. The control grid 14 and screen grid 16 comprise nested, cup-shaped cylindrical members mounted at their open ends to frustoconical supports 211 and 22, respectively. The grid supports 2@ and 22 are each provided with radially extending flanges between which an annular ceramic insulator Z4 is vacuum sealed. The anode 18 is also provided as a cylindrical cup member and is sealed at its open end to the screen grid support Z2 by a hollow cylindrical ceramic insulator 26 and a pair of anode contact cylinders Z8 and 30.

A hollow cylindrical cathode 12 comprises a woven mesh of thoriated tungsten filaments and is mounted conccntrically within the control grid 14 on a pair of concentric tubular conductive supports 32 and 34. The inner tubular support 32 extends past the end of the outer tubular support 34 and is provided with an outwardly extending, annular, cup-shaped iiange 36. One end of the cylindrical mesh cathode 12 is attached to the outer cylindrical surface 38 of the flange 36 andthe other end is attached in end-toend relation to an end of the outer tubular cathode support 34. The two tubular cathode supports 32 and 34 are in turn attached respectively -to a pair of radially flanged terminal members il and 42, which are insulatively mounted to the opposite flat sides of an intermediate annular ceramic insulator 43. The cathode assembly is sealed to the grid assembly by a weld between the lips of the terminal flange 42 and a cathode contact flange 44 brazed to a ceramic insulator ring 45 sealed to the lange of the control grid support 2G.

The electron tube 119 is closed at its base by a flanged cup base plate 46 which is welded to the anged terminal 4h. The base plate 46 supports `a getter structure 48 concentrically within the cathode assembly. The getter 48 comprises a tree-like structure and includes a support rod 50 which carries a plurality of sorptiontype getter disks S2 spaced therealong by spacer cylinders 54- interposed therebetween. A cup-shaped getter support S6 is attached to theflanged base plate 46 and supports the getter support rod at a distance from the base plate.

Cooling of the tube 1G is provided by .a series of heat radiating tins 53 secured to the external surface of the anode. The cooling fins 58 comprise a continuous metal strip which has been corrugated and wrapped around the anode. The inner folds of the strip are -brazed to the anode 18 and a thin securing cylinder 60 is crazed to the outer folds. Louvers 62 are stamped in the liat portions of each corrugation to provide improved yheat transfer characteristics.

ln the preferred fabrication procedure of the electron tube 1li incorporating my invention, a double-grid assembly, an anode assembly, and a cathode assembly are rst separately fabricated. The double-grid assembly includes the control and screen grids 14 and 16 mounted on their respective supports Ztl and 22, the intermediate ceramic insulator 24, the ceramic insulator 26, the inner anode contact cylinder 28, the ceramic insulator 45, and the cathode contact cylinder 44. The anode assembly includes the anode 18 and the outer anode contact cylinder 30. The cathode assembly includes the iilarnentary mesh 12, the concentric tubular conductors double grid assembly.

. A N 3 32 land 34, the cathode terminal anges 40 and 42, and the intermediate ceramic insulator 43.

The control and screen grids 14 and 16 are first provided as imperforate cup blanks attached to their supports 20 and 22. ,The control and screen grid blanks are .provided with central apertures 64 and 66, respectively 'through their end walls and are concentrically aligned by jigging on a-mandrel through these apertures. The other members of the double grid assembly are stacked and concentrically aligned with the grids, and the entire assembly is then sealed together by brazing in a furnace. The cylindrical walls of the imperfor-ate grid blanks are then provided with a series of longitudinal slots perfectly circumferentially aligned. According to a preferred practice, this is done by electric discharge machining through the imperforate cylindrical walls of both grid blanks with a single advance of a single tool.

The cathode assembly is fabricated by rst concentrically mounting the cathode tubular support cylinders 32 and 34 to the flanged terminals 40 and 42 and sealing vthe flanged terminals to the intermediate annular ceramic insulator 43. The hollow cylindrical thoriated tungsten mesh cathode 12 is then mounted to the annular cupshaped cathode ange 36 and to the free end of the outer tubular cathode support 34 in tandem relation therewith. The cathode assembly thus formed is enclosed in Ya benzene atmosphere and flashed according to known practices to provide a carbonized coating on the thoriated tungsten filaments. Subsequent to the carbonization `of VIthe cathode 12, the cathode assembly is inserted into the Y A stepped cylindrical jigging member is inserted into the open base end of the tubular cathode support conductor 32 and through apertures 64 and 66 in the end walls of the control and screen grids to concentrically align these three electrodes. A heliarc Weld is then made joining the lips of the terminal anges 42 and 44 to secure the cathode concentrically within the double-grid structure. After the weld has been completed, the cylindrical jig is removed.

The anode assembly is then joined to the combined cathode and grid assemblies by welding the lips of the inner and outer anode contact cylinders 28 and 30 together. Finally, the tube is closed by welding the lip of the flanged base plate 46, on which the getter structure 48 is mounted, to the lip of the terminal ange 40.

It will be appreciated that a number of advantages accrue from the novel double concentric tubular cathode support structure according to my invention. Since the two cathode lead-ins are provided by large concentric tubular conductors 32 and 34, and since the flanged base plate 46 is added to the tube 10 as the last step of fabrication, a relatively large unobstructed and easily accessible space is made available within and through the hollow cylindrical cathode 12. Accordingly, jigging of the cathode, control grid, and screen grid electrodes 12, 14, and 16 for concentricity can be performed internally of the tube rather than at the outer peripheries of their respective terminal anges 40-42, 20, and 22. This precludes dependence of the accuracy of jigging upon the size tolerances of the terminal ange members. Moreover, the jig member itself can be a much simpler and more accurately machined structure.

Possibly the most important advantage resulting from the novel concentric tubular cathode support structure is that the getter structure can be inserted in the space defined by the hollow cylindrical cathode 12 after activation of the cathode. In prior art structures the space within cylindrical cathodes has not been accessible completely to outside the tube envelope via a large tubular opening. This is true because of the conventional prior art practice of disposing center rod conductors or la- -ment support structures centrally between the cathode and the tube base.

Moreover, in accordance with known practices relating to the use of sorption-type getters, it is possible to extend the getter tree partially within the cathode and partially below the cathode This results in the desired feature of heating of the various getter disks 4S .to different temperatures. Accordingly, a variety of undesirable gases contained within the electron tube 10 are occluded by the different getter disks 52.

The double tubular lead-in and support structure for the cathode 12 also results in desirable radio frequency characteristics. Since the tubular cathode supports 32 and 34 are made straight without `any stepped cylindrical diameter variations, an extremely eicient RF lead to the cathode is provided. Such an RF lead-in to the cathode is least lossy since undesirable bends in the lead-in are avoided. Moreover, the providing of a relatively large diameter RF lead-in results in an excellent RF conductor since radio frequency energy passes mainly along the outer surface of a conductor.

The novel cathode support structure according to my invention, wherein an inner tubular member 32 extends through a hollow cylindrical cathode, provides an added advantage in that a heat retlector 68 is provided by the heater lead-in 32 without the necessity for a separate member. As is well known, the presence of a heat reflector insures the heat generated in the cathode by 12R losses will not be excessively lost.

It will be appreciated by those skilled in the art that the foregoing advantages accrue from the fact that the hollow cylindrical cathode 12 is supported by a pair of large concentric tubular lead-ins, one of which passes inside and through the cathode.

What is claimed is:A

l. An electron tube comprising a plurality of concentric cylindrical electrodes including a cathode and an anode, a pair of concentric tubular cathode supports, the inner one of said supports extending concentrically within said cathode, adjacent ends of said concentric supports being connected to opposite ends of said cathode, a base member sealed across and closing the other end of said inner concentric support, and a getter structure mounted on said base member concentrically within said inner concentric support and extending partly within said cathode, said getter structure comprising a rod mounted at one end on said base member and a plurality of sorption-type getter disks mounted on said rod and spaced therealong by a plurality of interposed spacer members.

2. An electron tube comprising concentrically disposed cylindrical anode, screen grid, control grid, and cathode electrodes, said screen grid and control grid electrodes each having a radially flanged tubular support, said cathode having a pair of radially flanged tubular supports, a plurality of annular ceramic insulators sealed between adjacent ones of said anges and between said screen grid ange and said anode, said tubular cathode supports being concentric and with one pair of adjacent ends thereof connected to opposite ends of said cathode, said cathode concentrically surrounding the inner one of said concentric supports and being substantially in tandem with the outer one of said concentric supports, and a sorption-type getter structure mounted concentrically within said inner concentric support on a platelike member sealed across and closing the flanged end of said inner concentric support.

3. An electron tube comprising concentric cup-shaped anode, screenl grid, and control grid electrodes nested in the order named and a hollow cylindrical cathode concentrically disposed within said control grid, said screen grid and control grid electrodes keach mounted at their open ends on the smaller ends on a pair of frustoconical supports, said frusto-conical supports having flat radially extending flanges at their larger diameter ends, a pair of concentric tubular Y cathode supports, one pair of adjacent ends of said tubular supports being connected to opposite ends of said cathode, the outer of said tubular supports being disposed substantially end 5 to end with said cathode yand the inner of said tubular supports extending through said cathode, said tubular supports being connected at their other pair of adjacent ends to a pair of annular flanges, annular ceramic insulators sealed between said anode and said screen grid support ange and between adjacent ones of said flanges of said screen grid, control grid, and outer and inner cathode supports, a base member sealed to and closing the anged end of said inner tubular support, and -a ber concentrically within said inner tubular support and extending partly into and partly out of said cathode.

References Cited in the tile of this patent tree-type sorption getter mounted on said base mem- 10 2,840,748

UNITED STATES PATENTS Wihtol Sept. 13, 1955 Katz Apr. 10, 1956 Lemagre-Voreaux June 4, 1957 Cherry June 24, 1958 

